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Acute Hepatopancreatic Necrosis Disease (AHPND) is an important limiting factor affecting the healthy cultivation of shrimp in recent years, which has brought huge economic losses to the global shrimp industry. In order to explore the relationship between the occurrence of AHPND and environment, pathogen and shrimp immunity factors, the pond cultured Litopenaeus vannamei systems were continuously monitored. Based on the 35 days continuously monitoring showed that, the air temperature, water temperature, dissolved oxygen (DO), pH, salinity, ammonia nitrogen (NH4-N) and nitrite (NO2-N) were fluctuated in the range of 21—29℃, 24.8—31℃, 1.4—8.32 mg/L, 8—8.91, 34—50, 0.01—0.26 mg/L and 0.005—0.212 mg/L, respectively; the culturable bacteria and Vibrio sp. in water and shrimp hepatopancreas were fluctuated in the range of 3×103—2.4×105 CFU/mL, 2×102—1.8×104 CFU/mL, 9.8×104—8.8×106 and 3.9×103—3.61×106 CFU/g, respectively; 135 isolates of Vibrio sp. were detected based on 16S rDNA, and the main Vibrio species was V. owensii, V. campbellii, V. parahaemolyticus, V. alginolyticus and V. harveyi; the activities of ACP, AKP, SOD, LZM and PO were 7.5—75, 1.0—8.5, 2.4—11.07, 1.3—43 and 23—28 U/mg, respectively. Combined the physical and chemical factors before and after the occurrence of AHPND, the results showed that, water temperature, culturable bacteria and Vibrio sp. in hepatopancreas, DO, LZM and PO could be used as the early warning candidate factors for the occurrence of AHPND in pond culture. The results provide a scientific basis for the healthy culture of L. vannamei and the prevention and control of AHPND disease.
In order to investigate the mechanism about the regulation of immune response by miRNAs mediating feed vitamin D3 in the JAK-STAT pathway of yellow catfish (Pelteobagrus fulvidraco), three diets with vitamin D3 content at 1120, 3950 and 16600 IU/kg were designed for juvenile Pelteobagrus fulvidraco. The growth trial was carried out over a 12-week period, following by an Edwardsiella ictaluri challenge experiment. Illumina high-throughput sequencing of head kidney and spleen after bacteria challenge identified differentially expressed miRNAs. The target genes of miR-194a was enriched in the JAK-STAT pathway. The relationship between miR-194a and the possible target genes jak2a and tyk2 had been verified by a dual luciferase reporter gene assay, which indicated the inhibitory role of miR-194a on jak2a and tyk2. In vitro, miR-194a was also found to respond with different concentrations of vitamin D3, inhibiting the expression of the target genes of jak2a and tyk2. With the activation of the JAK-STAT signaling pathway, the expression of anti-inflammatory response (AIR) factors and the target genes were also activated, the NF-κB pathway was inhibited, with significant decrease in expression of pro-inflammatory factors IL-1β, IL-6 and TNF-α and the transformation of macrophages from M1-type to M2-type polarization was accelerated with the increasing of vitamin D3 concentration (P<0.05). In conclusion, the results of this study demonstrated that miR-194a could respond to different concentration of vitamin D3 in vivo and in vitro experiments. Dietary vitamin D3 up-regulated the expression of miR-194a, which negatively regulated the target genes of jak2a and tyk2, and exerted indirect effects towards the downstream genes in the JAK-STAT pathway, illuminating the mechanism of miR-194a-mediated regulation of immune response by dietary vitamin D3 through the JAK-STAT signaling pathway in Pelteobagrus fulvidraco.
The aim of this study is to investigate the effects of different water velocities on the growth performance, antioxidant capacity, energy metabolism and tissue structure of Micropterus salmoides kept in an in-pond recirculation aquaculture (IPRA) system. 192 well-fed, healthy and uniformly sized largemouth bass [average weight: (8.13±0.82) g] were randomly assigned to 4 simulation tanks with 3 duplicates containing 16 fish each. The experiment was set up with a control group (a stagnant water group) and three water flow rate groups, namely, a low flow rate group (0.2 m/s), a medium flow rate group (0.4 m/s) and a high flow rate group (0.6 m/s), respectively, with a culture period of 154 days. The results were as follows: (1) WGR and SGR of largemouth bass in the medium flow rate group were significantly higher than those of the other three groups (P<0.05), while the SGR of the high flow rate group was significantly lower than that of the other three treatment groups. The CF was significantly lower in the medium and high flow rate groups than that in the stagnant water and low flow rate groups. The visceral adiposity index (VAI) of largemouth bass decreased significantly with the increasing of flow rate (P<0.05). (2) The crude protein levels of muscle were significantly higher in the medium flow rate group than that in the other three groups. The crude fat content of muscle was significantly higher in the stagnant water and low flow rate groups than that in the medium and high low rate groups. The amount of crude fat in the specimens decreased significantly with an increased flow rate of water (P<0.05). (3) Serum triglycerides and the total amount of cholesterol in the specimens were significantly lower in the medium and high flow rate groups than that in the stagnant water and low flow rate groups (P<0.05). The concentration of free fatty acids and total amount of protein were significantly lower in the high flow rate group than that in the other three groups (P<0.05). (4) SOD and CAT increased with the increasing of the water flow rate, with the highest SOD level in the livers of the specimens in the medium flow rate group and there was a significantly higher concentration of serum CAT in the high flow rate group than the other three groups (P<0.05). Serum and liver tissue MDA levels were significantly lower in the medium flow rate group than that in the other three groups (P<0.05). The AOC of serum and liver tissues were significantly higher in the medium flow rate group than that in the other three groups (P<0.05). (5) LPS activity increased significantly in the specimens tested with an increased flow rate (P<0.05). AMS and PTS activities were the highest in the medium flow rate group. Hepatic LPS activity was the highest in the medium flow rate group, which was significantly higher than that in the stagnant water and low flow rate groups (P<0.05). PTS activity was significantly higher in the medium and high flow rate groups than that in the low flow rate groups. GDH increased significantly with the increased flow rate in both the muscles and liver (P<0.05). (6) The diameter of muscle fibres in the low flow rate group was significantly higher than that in the other three treatment groups (P<0.05). The density of muscle fibres increased significantly with an increase of water velocity. The medium flow group improved the tissue structure, while the high flow group caused some damage to their liver cells. In conclusion, the medium flow rate group with a flow rate of 0.4 m/s can promote the growth of largemouth bass, boost the immune systems, improve the functioning of their metabolisms, increase the crude protein content and inhibit fat deposition, and should be used as the optimal water flow rate for IPRA.
Mandarin fish (Siniperca chuatsi) is a kind of carnivorous fish that feeds on live prey fish. Recent research has shown that it could be domesticated by artificial diet. However, the effects of artificial diet feeding after domestication on the nutritional value and flesh quality were lacking. The present study compared nutritional composition, amino acid component and its nutritional evaluation, fatty acid profiles, and texture properties between mandarin fish fed with live prey fish and artificial diet. The results showed that no significant differences were observed in the protein levels of the two groups, while the lipid levels were significantly higher in fish fed the artificial diet (P<0.05). The amino acid score (AAS), chemical score (CS), essential amino acid index (EAAI) and F value did not vary between groups. However, Met+Cys were both the first-limiting amino acids in mandarin fish under the two feeding modes, which could provide information to improve diet formulation. The levels of unsaturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) were extremely significantly higher in mandarin fish fed an artificial diet (P<0.01), especially for the levels of C20﹕5 (EPA) and C22﹕6 (DHA), which indicated that artificial diet feeding could provide better fatty acid profiles than live prey fish by balanced diet formulation. The firmness, chewiness, gumminess, and resilience in the muscle of mandarin fish fed with artificial diet were extremely higher than the live prey fish group (P<0.01), whereas the stickiness showed the opposite levels (P<0.01), suggesting the improvement on texture of flesh quality. Overall, we found no variations in protein levels and amino acid evaluations in mandarin fish fed the artificial diet, but the fatty acid profiles showed superior results as indicated by higher levels of EPA and DHA. Therefore, our findings evaluated the flesh quality properties of mandarin fish by feeding an artificial diet, showing the potential of the use of an artificial diet in mandarin fish and the sustainable development of its industry.
Ammonia nitrogen, as one of the main pollutants, have toxicity to organisms under high concentration in aquatic ecosystem. It has been widely reported about the negative impacts of ammonia on the behavior, growth and reproduction of organisms. However, the previous studies were mainly focused on fish, rarely studies were conducted with zoobenthos and limited to small scale experiments. To explore the toxicity of ammonia on zoobenthos, we conducted a one-year semi-natural experiment in 6 ponds (ca. 600 m2 in surface area; ca. 1.5 m in depth) located in Hubei Province and analyzed the difference of zoobenthos (mollusc) community under 6 ammonia concentrations [N25>N20>N15>N10>N5>N0 (control; 0.2—33.7 mg/L]. The result showed that: (1) the mollusc identified during the experiment was mainly Bellamya aeruginosa; (2) N0, N5, N10 and N15 treatments had similar B. aeruginosa density [28(0—85) ind./m2], which were significantly higher than that in N20 and N25 treatments [5(0—29) ind./m2] (P<0.05); (3) N0, N5, N10, N15 and N20 treatments had similar B. aeruginosa biomass [40.0(0—85.5) g/m2], which were significantly lower than that in N25 treatment [0.8(0—4.0) g/m2] (P<0.05); (4) shell length, shell width and body mass of B. aeruginosa were the lowest in N0 treatment, while which were the highest in N20 or N25 treatment; (5) B. aeruginosa density and biomass were negatively correlated with ammonia concentration significantly (P<0.05), and decreased with the increasing non-ionized ammonia concentration; (6) shell length, shell width and body mass of B. aeruginosa were positively correlated with non-ionized ammonia concentration significantly (P<0.05), and increased with the increasing nonionized ammonia concentration. The results suggested that ammonia concentration higher than 21.7 mg/L and non-ionized ammonia concentration higher than 0.18 mg/L (annual mean value in N15 treatment) had significantly negative impact on mollusc, especially for its reproduction, while no negative impact was found on the growth of individuals. More phytoplankton induced by ammonia loading may provide more food for mollusc which was advantageous for the accumulation of carbohydrate and help to detoxify the body. The shelter from sediments might have released B. aeruginosa from ammonia exposure as the non-ionized ammonia concentration was lower at the bottom layer near the water-sediment interface compared with that at the surface layer. This study could help to develop the understanding of ammonia toxicity to mollusc and may improve scientific basis for nitrogen management in aquatic ecosystems to a certain extent.
Nitrogen and phosphorus are limiting and essential macronutrients to maintain the growth of phytoplankton, and monitoring their changes are fundamental to lake management. The relationship of TN and phytoplankton chlorophyll a (Chl. a) was reported in some research; however, TN may be underestimated in some research due to measurement errors in bloom-occurring water bodies. The alkaline potassium persulfate digestion-UV spectrophotometry method is widely used for water quality determination for TN. The organic nitrogen in cyanobacterial cells may be difficult to be completely degraded, which should result in the underestimation of TN. However, there is no detailed study on TN determination of bloom water containing high-density algal cells.The TN was underestimated by directly measuring the samples from Taihu Lake, although the TN was within the allowable concentration range of the standard method (<7.0 mg/L, HJ636-2012). In order to explore the effect of cell densities on TN determination, the lab-cultured cyanobacterium and green algae was measured. The results showed that TN of high-density cells was significantly underestimated. The density of cells must be less than 108/L to meet the requirements of accurate TN determination. We measured several samples from natural blooms to estimate the TN in the Microcystis blooms. The TN value obtained from the original water sample was underestimated by 26.59%—40.42% compared to the measured value of the water sample diluted 10—30 times. Our results demonstrated that sufficient dilution is necessary for the TN measuring of cyanobacterial blooms.In order to estimate the contribution of Microcystis biomass to TN, the TN and Chl. a in four bloom samples collected from Taihu Lake were measured. The mean value was 0.15 mg N/μg Chl. a (spiked recovery rate was 98.84%—109.39%). The average nitrogen content of dry Microcystis blooms from Taihu Lake was about 16%. These data should be useful for the ecological research of and the control of Microcystis blooms.
Microcystis blooms are common in eutrophic water bodies in China. Some Microcystis species can produce microcystins (MCS), which pose a serious threat to the safety of humans and ecosystems. The anionic surfactant linear alkylbenzene sulfonate (LAS), as a kind of widespread organic pollutant in eutrophic water bodies, its potential effects on the succession of toxic and non-toxic Microcystis and its influence on the toxicity of toxic Microcystis are often ignored. The effects of different LAS concentrations (0, 0.05, 0.2, 0.5, 1.0 and 5.0 mg/L) on the growth, photosynthetic characteristics, interspecific competition and toxin synthesis of toxic Microcystis aeruginosa and non-toxic Microcystis wesenbergii were studied in the present study. The results showed that the biomass, mcyD expression and MCs content of the toxic Microcystis increased significantly after 12 days of culture at 0.05—5.0 mg/L LAS. The concentrations of intracellular and extracellular MCs in toxic Microcystis were 0.069, 0.052, 0.061, 0.038, 0.037 fg/fg chl.a and 107.1, 103.7, 127.1, 99.6 and 113.7 ng/L, respectively. 0—0.2 mg/L LAS had no significant effect on the biomass of Microcystis wesenbergii, while a higher concentration of LAS (0.5—5.0 mg/L) significantly inhibited the growth of non-toxic Microcystis wesenbergii. When two Microcystis strains were co-cultured, the expression of mcyD in Microcystis aeruginosa responded quickly to LAS, the proportion of toxic Microcystis aeruginosa in the total Microcystis up to 60%—80%. But the synthesis and release of MCs were slow. A large number of MCs were synthesized and released after 12 days of co-culture. The intracellular MCs content was 0.098, 0.184, 0.201, 0.216, 0.168 and 0.241 fg/fg chl.a, respectively. In general, this research showed that LAS could promote the growth and toxin synthesis of toxic Microcystis. Therefore, the potential role of LAS pollution on the dominance formation of toxic Microcystis and toxin of blooms in eutrophic water can not be ignored.
To investigate the effect of LED light on the photosynthetic activity of cyanobacteria, the photosynthetic activity of Microcystis aeruginosa PCC 7806 was examined after 2h of LED treatment with different light quality and intensity using 25 μmol photons/(m2·s) of white fluorescent light as control. When compared to the control, results indicated that the cell photosynthetic activity (Fv/Fm) soared significantly under 25—50 μmol photons/(m2·s) LED red and blue light, and 25—100 μmol photons/(m2·s) LED white and green light treatments. LED red and blue light significantly inhibited cell photosynthetic activity at 100 μmol photons/(m2·s), whereas this intensity was more than 200 μmol photons/(m2·s) for the LED white light and 500 μmol photons/(m2·s) for the LED green light, and the maximum photochemical efficiency of photosystem Ⅱ (PSⅡ) Fv/Fm, the electron transfer rate ETR (Ⅱ) and light quantum yield Y (Ⅱ); the photosystem Ⅰ (PSⅠ) electron transfer rate ETR(Ⅰ), and the light quantum yield Y(Ⅰ) decreased with increasing light intensity; with increasing light intensity, the degree of electron transfer blockage between
The Cladophora overgrowth has become a widespread global problem. The decomposition of Cladophora biomass releases large amounts of dissolved organic matter (DOM), a key substance in the biogeochemical cycle of carbon in aquatic ecosystems, resulting in a more complex organic pollution in water bodies. Field investigations and indoor experiments have proven that one of the sources of endogenous DOM in water bodies is the biodegradation of algae. Microorganisms play an important role in the decay of aquatic plants, and bacteria differ in their metabolic preferences and affinity for substrates. Bacterial diversity and community composition may both influence and respond to changes in DOM. However, it is not clear how the microbial community and the DOM composition of the surrounding water column change during the decomposition of the Cladophora. In order to study the composition of algal-derived DOM, we simulated the decay process of Cladophora in the laboratory. The experiment was carried out in a constant temperature incubator. 10 g (fresh weight) of Cladophora was placed into sterile polyethylene plastic bottles with 500 mL of sterile water and placed in dark conditions at 25℃ to decay naturally. Three replicate samples were randomly selected for chemical and microbiological analysis at 1, 4, 7, 10, 15, 20, 30 and 40 days. We performed 16S amplicon sequencing of algal-attached microorganisms to analyse the dynamic process of microbial self-assembly on decaying algae. The results showed that during the 40-day decomposition experiment, the biomass of Cladophora decreased, and it showed a trend of rapid loss in the early stages and slowed down in the later stages. At the end of the experiment (40 days), the dry matter residual rate was 43.15% and the mass loss was 56.85%. During the decomposition process of Cladophora, DOM quickly released to the maximum within 7—10 days. The composition of DOM also became complicated, and the fluorescence peaks gradually shifted from regions Ⅰ, Ⅱ and Ⅳ to regions Ⅲ and Ⅴ. A large amount of simple aromatic proteins, such as tyrosine, were transformed into various metabolites by microorganisms, and humic substances were produced. The dominant phyla of microorganisms attached to the Cladophora were Proteobacteria, Bacteroidetes and Firmicutes, with relative abundances ranging from 6.54% to 71.62%, 16.83% to 55.50% and 0.95% to 20.91%, respectively. In different stages of the decay process, the composition of microorganisms was significantly different, which was mainly dominated by Proteobacteria in the early stage and Bacteroidetes in the late stage of the experiment. Pearson's correlation (R=0.81, P=0.001) between Bray-Curtis distance and Euclidean distance of DOM composition for bacterial communities was calculated using the Mantel test (999 ranking). The results of the Mantel test indicated that changes in DOM composition were significantly correlated with changes in the composition of the bacterial community. These findings have implications for further understanding of the characteristics of DOM released during the decay of Cladophora blooms and the relationship between DOM and microbial communities, and provide theoretical support for the management of filamentous green algae blooms.
Chromochloris zofingiensis can achieve ultra-high cell density and simultaneously accumulate astaxanthin under heterotrophic conditions, however, the relatively low cellular astaxanthin content of C. zofingiensis hinders its commercial application. With the aim to improve the ellular astaxanthin content of C. zofingiensis, this study screened a mutant 12C10 with enhanced astaxanthin content from the mutant library established by using ethylmethylsulfone mutagenesis. The astaxanthin content of 12C10 was 74% higher than that of the wild type under the heterotrophic normal conditions, and 25% higher than that of the wild type at day 4 under the nitrogen deficiency conditions. Additionally, the results of the widely targeted metabolomics analysis revealed the differences in the metabolites level between 12C10 and wild type under the normal conditions. Specifically, the contents of fatty acids and amino acids except glutamate generally decreased, but the content of glutamate significantly increased in 12C10 compared to wild type. Reduced synthesis of amino acids and fatty acids in 12C10 can provide more carbon skeleton, NADPH, and ATP for astaxanthin synthesis. The accumulation of glutamate on the one hand may stimulate the activity of glucose 6-phosphate dehydrogenase in pentose-phosphate pathway to produce more NADPH, and cause production of reactive oxygen species to trigger astaxanthin synthesis. The metabolome analysis also showed that the enhanced astaxanthin synthesis in 12C10 may be related to the enhanced ethylene synthesis. This study lays the foundation for improving C. zofingiensis astaxanthin content through metabolic regulation in the future, and is of great significance for guiding the development of the new processes of C. zofingiensis astaxanthin accumulation.
As an important raw material for the extraction of natural astaxanthin, Haematococcus pluvialis is usually harvested by natural sedimentation or centrifugation. However, these harvesting methods either take a long time or consume a lot of energy. This study proposed an efficient method for the harvesting H. pluvialis using pH-induced induced dissolved air flotation (DAF). Harvesting efficiency and solid content, as well as their kinetic curves, were adopted to investigate the influence of pH on the pH-induced DAF harvesting. In addition, the harvesting performances of pH-induced DAF was compared with those of pH-induced sedimentation, chemical coagulant (aluminum sulfate)- and biological coagulant (chitosan)-induced DAF, based on the efficiency and residual metal contents in the harvested biomass. Whether pH treatment affects the astaxanthin content in the harvested biomass was also evaluated, comparing with the content in centrifugation harvested biomass. The results showed that auto-flocculation occurred when the pH of the media was decreased or increased, facilitating the flotation harvesting and sedimentation harvesting of H. pluvialis. pH-induced DAF obtained higher harvesting efficiency and required less separation time, comparing with pH-induced sedimentation. When pH was adjusted to less than 3 or greater than 11.5, the harvesting efficiency of 95% was achieved in 2min using pH-induced DAF, while that took 30min for pH-induced sedimentation to achieve 80%—90% harvesting efficiency. When the initial concentration was 3.2 g/L, the solid content of biomass harvested by pH-induced DAF can reach 17%, realizing 53 times concentration, which was much higher than those harvested by pH-induced sedimentation. Most importantly, pH-induced DAF performed as well as aluminum sulfate and chitosan coagulants induced DAF, while avoiding the impurity of biomass caused by chemical such as Al3+. The astaxanthin contents in H. pluvialis biomass harvested by pH-induced DAF were not affected by the pH treatment. Therefore, harvesting H. pluvialis by pH-induced DAF proved to be a rapid, efficient and environmental sustainable technique, which shed a light on the process development of mass production of H. pluvialis biomass.
Euglenaria Karnkowska, Linton & Kwiatowski is a new genus isolated from Euglena Ehrenberg in 2010. Currently, there are 4 species reported in the world. In China’s existing algal taxonomic data, the species of Euglenaria are still classified in Euglena, and their morphological description is vague, making it difficult to distinguish them from some species of Euglena. It is difficult to identify Euglenaria and Euglena, and there is no obvious difference between Euglenaria and some species of Euglena in morphology. With the development of molecular biology, new technical means have been brought for the identification of euglenoid. While further research on the systematic classification of euglenoid has been carried out, the classification status of many euglenoid species has been revised, and Euglenaria is a new genus separated from Euglena at this stage. Our study found that the cells of Euglenaria are generally fusiform without mucocysts, and the Chloroplasts are disc-shaped with pyrenoids and edges irregular with deep grooves. The morphological differences among the species of Euglenaria are mainly reflected in the shape, number of chloroplasts and size of cells. The cells morphology of Eu. clepsydroides are hourglass shaped. The cells of Eu. caudata [length (58.95±12.38) μm, width (28.57±5.82) μm] were the largest. The chloroplast number of Eu. anabaena and Eu. clavata was significantly different. Eu. anabaena contained fewer chloroplasts (only 4±1), while Eu. clavata cells contained 10±3 chloroplasts. The morphological differences among species of Euglenaria are very subtle, and it is difficult to correctly identify them. The phylogenetic tree showed that with the closely related Eutreptiaceae as the outgroup, the results indicated that the rest of the euglenoids were divided into two major clades, the Euglenaceae clade and the Phacaceae clade. Euglenaceae (0.96/597) included Euglenaformis, Strombomonas, Trachelomonas, Cryptoglena, Euglena, Monomorphina, Euglenaria and Colacium. Each genus formed a well-supported evolutionary clade, respectively. The genus Euglenaria is located in the branch of Euglenaceae (0.84/-), consisting 28 strains of Euglenaria, which are divided into 3 subbranches, and the support rate of each subbranch exceed 99%. Eu1 clade contained 13 strains of Eu. anabaena, Eu2 (1.00/998) contained 8 strains Eu. caudata, and Eu3 (1.00/1000) contained 6 strains Eu. clavata. Eu. anabaena and Eu. caudata were sister branches. However, there are great difference in cell size and chloroplast number between the two species. In morphology, Eu. anabaena and Eu. clavata were more similar, with similar cell size and large difference in chloroplast number. There were significant differences in cell size between Eu. caudata and Eu. clavata, but the number of chloroplasts was similar. This suggests that the relationship between morphology and molecular phylogeny may be inconsistent. At present, there are only 4 species of Euglenaria and 162 species of Euglena, and 80% species of Euglena have no molecular data. It is unknown whether there are still Euglena species belonging to Euglenaria among these species without molecular data, and further research is still needed. In this study, 12 strains of Euglenaria collected from China were used as materials to study the phylogeny of Euglenaria based on morphological and molecular biological methods. We provide the Euglenaria species in morphological characters and molecular data and discusse the phylogenetic position of Euglenaria. In order to improve the taxonomic description of this group in China, we revised the taxonomic description of Euglenaria.
In order to assess the current situation of fish resources in the Provincial Nature Reserve for Yangtze Cetacean of Zhenjiang, a simultaneous survey of fish resources was carried out in spring (April) and autumn (September) in 2020 by using hydroacoustic frequency difference technology and net survey method, and the temporal and spatial characteristics of fish resources in the surveyed river section were evaluated. Based on the analysis of fish echo image data of 200 and 333 kHz, the acoustic assessment of fish resources was carried out by frequency difference technique. The results of hydroacoustic survey showed that the average density of fish resources was (0.094±0.183) ind./m2, and the average target strength (TS) of fish was (–57.33±5.69) dB, mainly distributed in the range of –62.5 to –50.5 dB. In addition, TS increases with increasing water depth. The results of net survey showed that 758 fishes (53.53 kg) were collected in the river section and a total of 48 species were identified, of which Cypriniformes dominated. The proportion of pelagic fish population quantity and mass was 36.15% and 66.12%, respectively. The proportion of the quantity and mass of fish (pelagic fish with body length less than 20 cm, body height less than 6 cm and body weight less than 100 g) fed on the Yangtze finless porpoise was 23.22% and 8.72%, respectively. In terms of time characteristics, there was no significant difference in fish resource density between April and September (P>0.05), and the average TS in April was smaller than that in September, and the average size of fish in April was smaller than that in September. In terms of spatial characteristics, the fish resources were mainly distributed in the waters near the north branch of He Changzhou and Jiaobei Beach, and the pelagic fish resources were relatively large, and the fish resources were more concentrated in April. Underwater acoustic frequency difference technology can effectively eliminate plankton signals and background noise signals in the water environment, which is of reference significance for fishery acoustic evaluation in the Yangtze River Basin. The results of this study can provide a scientific basis for the accurate assessment of the bait fish resources of the Yangtze finless porpoise in the reserve, support the conservation of the Yangtze finless porpoise in situ, and provide a scientific basis for the conservation of fish resources in the lower Reaches of the Yangtze River.
In the middle-lower reach of the Yangtze River, there are many lakes with intensive fish biodiversity, which are connected with the Yangtze mainstream historically. Since the 1950s, most of these lakes have experienced river-lake disconnection by anthropogenic impacts, leading to remarkable biodiversity decline of fish in these lakes. Based on the published literatures about fish assemblages in lakes, the taxonomic distinctness and temporal changes of fish communities in the connected lakes and disconnected lakes were examined by using two taxonomic diversity indices (average taxonomic distinctness, Δ+ and variation in taxonomic distinctness, Λ+), to assess the impact of river-lake disconnection. The results indicated that disconnected lakes showed significantly lower species richness and Δ+ values (average values of 48.47±14.64 and 74.02±3.093, respectively) than connected lakes (average values of 76.22±14.40 and 78.31±0.98, respectively; P<0.001), indicating the loss of fish diversity. On the contrary, the disconnected lakes showed significantly higher Λ+ values (average values 736.89±33.80) than connected lakes (average values of 697.31±25.53; P=0.002), indicating the increasing unevenness of taxonomic distinctness. Our analysis of temporal changes showed that species richness and Δ+ generally declined, and Λ+ generally increased through time within representative connected and disconnected lakes. However, the species richness, Δ+ and Λ+ values of the connected lake fluctuated over time, and the Λ+ increased significantly over time. These mean that connected lakes were also affected by various disturbances, which led to the decline of taxonomic diversity and the distribution of fish in disconnected lakes was more concentrated in some taxa resulting high unevenness and low stability in the community. Based on our results, we suggested to restore the fish diversity in the middle and lower reaches of the Yangtze River by recovering the connection between the lakes and the Yangtze mainstream, improving the quality of fish habitat through water environment management, and scientifically adjusting the fish community structure.
Poyang Lake is the largest freshwater lake in China, and a typical natural lake in the middle and lower reaches of the Yangtze River. Different habitat season landscapes can meet the needs of fish in different life history stages, so that fish resources show dynamic distribution characteristics. The 10-year fishing ban have been implemented in the Yangtze River basin, including Poyang Lake since Jan 1, 2021, to conserve the aquatic organism of the Yangtze River. In this study, we applied hydroacoustic analysis with Simrad EY60 split-beam echo sounder, to detect the spatial-temporal distribution of fish in Poyang Lake from 2020 to 2021. The results showed that more than half of the fish were 10—30 cm of body length in all three seasons, deduced from the fish target strength (TS) signal. However, the TS varied significantly among seasons (P<0.05), with the highest TS in winter (–51.0±14.13) dB and the lowest (52.71±9.95) dB in autumn. The horizontal distribution of fish density was not homogeneous, and also significantly different among seasons (P<0.01). The maximum density was 440.22, 169.19, and 554.18 ind./1000 m3 in autumn, spring, and winter, respectively. Vertically, the fish density decreased gradually from the bottom to the surface in autumn and winter, while the fish density in the surface and middle layers was higher than that in the bottom in spring. The fish density varied significantly in the same water layer among seasons (P<0.01). This study obtained the spatial and temporal distribution characteristics of fish in Poyang Lake by using hydroacoustic method at the beginning of fishing ban, and provided a reference for the study of fish resource in the region at a macro spatial scale under natural conditions. The results can also support for the evaluation of the fishing ban effect and the evaluation of biological integrity during the ten-year fishing ban in Poyang Lake.
In order to elucidate the changes in the components and contents of fatty acid of female Coilia nasus in the Yangtze River during spawning migration process, the components and contents of various fatty acid in the hepatopancreas, muscle and ovary of Coilia nasus were determined from three aspects of migration distance, ovarian development and body length. The results showed that 28 kinds of fatty acids were detected in the three tissues of 62 female Coilia nasus, including 8 saturated fatty acids (SFA), 6 monounsaturated fatty acids (MUFA) and 14 polyunsaturated fatty acids (PUFA). Among all the fatty acids, MUFA were the most abundant, accounting for more than 56.23% of the total fatty acids in each tissue. Specific fatty acids with higher levels included C18﹕1, C16﹕0, C16﹕1, DHA and EPA. During migration, the total amount of fatty acids in the hepatopancreas of Coilia nasus increased from (526.61±38.50) mg/g in Chongming to (587.21±124.72) mg/g in Anqing, but decreased by 33.03% and 57.09% in muscle and ovary respectively. The total amount of fatty acids, SFA, MUFA and PUFA in muscle were positively correlated with body length (P<0.05), but the contents of total fatty acids and fatty acids components in hepatopancreas and ovary had no significant correlation with body length (P>0.05). During the ovarian development from stages Ⅱ to Ⅳ, the contents of total fatty acids in hepatopancreas and muscle decreased by 47.56% and 22.40%, respectively, but increased from 364.17 to 418.95 mg/g in ovary. The contents of C18﹕1, EPA and C16﹕1 in hepatopancreas and muscle decreased, but increased by 1.21, 1.36 and 1.31 times in ovary (stages Ⅱ to Ⅲ), respectively, indicating that these fatty acids were also significantly transferred during ovarian development. The present study also found that there were more fatty acids in muscle of large size Coilia nasus, the abundance of SFA and MUFA in each tissue, and EPA and DHA in the ovaries, which provided sufficient nutrition for migration activities and gonad development.
The Yangtze River estuary is the major production regions of larval eels in China, and it is also the most important place for feeding and nursing place for fishes. In order to clarify the species diversity and damage rate of fishes by-catch in elver nets in the Yangtze Estuary, this article analyzed 11870 fish samples collected by elver nets during the eel fry flood season from 2017 to 2019. The results showed that 43 samples contained 114388 fishes by-catch in elver nets, 54 species were identified, belonging to 13 orders, 27 families and 46 genera. Among them, Perciformes accounted for 40.74% of the total species, and marine, carnivorous, demersal and small fishes accounted for 44.44%, 74.07%, 70.37% and 48.15%, respectively. Odontamblyopus lacepedii was the first dominant species, accounting for 77.07%; Cynoglossus joyneri, Coilia nasus and Konosirus punctatus were also the dominant species in individual years. According to the difference of fish assemblage, March and April, January and February can each be combined into one group. The major characteristic species of two groups were 5 and 6, and the major divergent species were 10. The average body length was (73.77±38) mm of 54 species. Fish resources of the early life history stages account for 96.65% of the total samples, many of which are larvae of local economic fishes. There were 16470 eel elvers in the sample, and the average damage rate of fishes by-catch in 3 years was 7.58, which was higher than 6 years ago. Attention should be paid to the damage caused by fishing eel elvers to other fishes’ larvae.
Cyanobacterial blooms worldwide pose severe threat to aquatic ecosystem functions and even human health. Due to environmental-friendliness and high selectivity, allelochemicals have put forward a promising option for inhibiting cyanobacterial overgrowth and therefore mitigating blooms in a short term. This study overviewed the algicidal effects of four types of allelochemicals, i.e., polyphenolics, nitrogen-containing compounds, fatty acids/esters and terpenoids, as well as underlying mechanisms and specific target sites against cyanobacteria, and further evaluated the application potential based on economic costs of highly effective cyanobacterium-inhibiting allelochemicals. The results demonstrated distinctive algicidal characteristics among each type of allelochemicals: Fatty acids/esters were the most cost-effective in algicidal activity, which induced extremely strong toxicity to cyanobacteria at low doses due to various action targets and suppressed target cyanobacterial growth by 50% in concentration range of 0.015—52.95 mg/L; Polyphenolics as the most abundant allelochemicals generally exhibited high algicidal activity with median effect concentration (EC50) ranging from 0.05 to 162.53 mg/L, and could restrain cyanobacterial growth by multiple mechanisms such as inhibiting photosynthesis, disrupting cellular oxidative stress balance and damaging cell wall/membrane structure. However, the theoretical costs vastly differed among highly effective algicidal polyphenolics, whose cost-efficiencies were inferior to fatty acids and thus ranked as 2nd place following fatty acids; N-containing compounds generally exhibited specific and evenly effective algicidal effect against cyanobacterial growth, with EC50 varying from 0.3 to 8.14 mg/L, and induced irreversible cell damage by mainly disrupting cyanobacterial photosynthesis, blocking electron transfer, and destroying cellular structures (including ultrastructure). However, N-containing compounds involved high costs and lowest effectiveness that hindered their wide application. Terpenoids exhibited relatively weak algicidal effect as compared to other three types of allelochemicals, which exerted algicidal effect through multi-routes to mainly disrupt photosynthetic function of cyanobacterial cells, with higher EC50 reaching up to 25.3—228 mg/L that limited their actual application. Consequently, this review summarized joint action effect modes and characteristics of same type and different types of allelochemicals on cyanobacterial (mainly Microcystis aeruginosa) growth to decrease applying dosages of allelochemicals, diminish economic costs and achieve more efficient algicidal effects, and pointed out that allelochemicals number in mixture, action target sites, each allelochemical proportion in mixture and mixture dosage were key factors to determine joint action effect of mixed allelochemicals. This review also proposed that different allelochemicals with diverse and complementary action target sites (referred as ‘multi-target mixture’) could exert synergistic effects, and that proportions of allelochemicals with high algicidal activity should be increased in mixture (referred as ‘new-barrel effect’ synergistic effect). Moreover, this review also proposed that multiple allelochemicals were more likely to arouse synergistic algicidal effects when they were mixed based on their inherent types, contents and proportions actually excreted by plants, which provided novel insights for scientific, comprehensive and reasonable choice, application and optimally mixing of allelochemicals, in controlling cyanobacterial blooms.